With the small signal models coming out, the next step is to calculate the compensation network parameters with the given inductor and output capacitance.

1. Set the Crossover Frequency, ƒ_C.
   • The first step is to set the loop crossover frequency, ƒ_C. The higher crossover frequency, the faster the loop response is. It is generally accepted that the loop gain cross over no higher than the lower of either 1/10 of the switching frequency, ƒ_SW, or 1/5 of the RHPZ frequency, ƒ_RHPZ. Then calculate the loop compensation network values of R_c, C_c, and C_p in following sections.
2. Set the Compensation Resistor, R_C.
   • By placing ƒ_Z below ƒ_C, for frequencies above ƒ_C, R_C | | R_EA approximately = R_C, so R_C × G_EA sets the compensation gain. Setting the compensation gain, K_COMP-dB, at ƒ_Z, results in the total loop gain, T_(s) = G_PS(s) × H_EA(s) × He(s) being zero at ƒ_C.
   • Therefore, to approximate a single-pole rolloff up to f_P2, rearrange Equation 19 to solve for RC so that the compensation gain, K_EA, at f_C is the negative of the gain, K_PS, read at frequency f_C for the power stage bode plot or more simply:
     Equation 19.

     where

     • K_EA is gain of the error amplifier network
     • K_PS is the gain of the power stage
     • G_EA is the transconductance of the amplifier, the typical value of G_EA = 175 µA / V
3. Set the compensation zero capacitor, C_C.
   • Place the compensation zero at the power stage pole position of R_OUT, C_OUT to get:
     Equation 20.
   • Set ƒ_Z = ƒ_P, and get:
     Equation 21.
4. Set the compensation pole capacitor, C_P.
   • Place the compensation pole at the zero produced by the R_ESR and the C_OUT. It is useful for canceling unhelpful effects of the ESR zero.
     Equation 22.
     Equation 23.
   • Set ƒ_P2 = ƒ_ESR, and get:
     Equation 24.
   • If the calculated value of C_P is less than 10 pF, it can be neglected.
   Designing the loop for greater than 45° of phase margin and greater than 6-dB gain margin eliminates output voltage ringing during the line and load transient. The R_C = 61.9 kΩ , C_C = 680 pF for this design example.